NASA Satellites Show Drought May Take Toll on Congo Rainforest
PR Newswire
WASHINGTON, April 23, 2014
WASHINGTON, April 23, 2014 /PRNewswire-USNewswire/ -- A new analysis
of NASA satellite data shows Africa's Congo rainforest, the
second-largest tropical rainforest in the world, has undergone a
large-scale decline in greenness over the past decade.
The study, led by Liming Zhou of University at Albany, State
University of New York, shows between 2000 and 2012 the decline
affected an increasing amount of forest area and intensified. The
research, published Wednesday in Nature, is one of the most
comprehensive observational studies to explore the effects of
long-term drought on the Congo rainforest using several independent
satellite sensors.
"It's important to understand these changes because most climate
models predict tropical forests may be under stress due to increasing
severe water shortages in a warmer and drier 21st century climate,"
Zhou said.
Scientists use the satellite-derived "greenness" of forest regions as
one indicator of a forest's health. While this study looks
specifically at the impact of a persistent drought in the Congo region
since 2000, researchers say that a continued drying trend might alter
the composition and structure of the Congo rainforest, affecting its
biodiversity and carbon storage.
Previous research used satellite-based measurements of vegetation
greenness to investigate changes in the Amazon rainforest, notably the
effects of severe short-term droughts in 2005 and 2010. Until now,
little attention has been paid to African rainforests, where ground
measurements are even sparser than in the Amazon and where droughts
are less severe but last longer.
To clarify the impact of long-term drought on the Congo rainforest,
Zhou and colleagues set out to see whether they could detect a trend
in a satellite measure of vegetation greenness called the Enhanced
Vegetation Index. This measure is developed from data produced by the
Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on
NASA's Terra satellite. The scientists focused their analysis on
intact, forested regions in the Congo basin during the months of
April, May and June each year - the first of the area's two peak rainy
and growing seasons each year.
The study found a gradually decreasing trend in Congo rainforest
greenness, sometimes referred to as "browning," suggesting a slow
adjustment to the long-term drying trend. This is in contrast to the
more immediate response seen in the Amazon, such as large-scale tree
mortality, brought about by more episodic drought events.
The browning of the forest canopy is consistent with observed
decreases in the amount of water available to plants, whether that is
in the form of rainfall, water stored in the ground, water in
near-surface soils, or water within the vegetation.
These changes in available water were detected in part with NASA
satellites including the NASA/JAXA Tropical Rainfall Measuring
Mission, NASA's Quick Scatterometer (QuikScat), and NASA's Gravity
Recovery and Climate Experiment, a joint mission with the German
Aerospace Center.
"Combining measurements from different sensors has given us more
confidence in the results of the MODIS data and provided us with
insights into the environmental and physiological mechanisms of the
browning observed by the MODIS data," said co-author Sassan Saatchi of
NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif.
Climate factors known to affect vegetation growth were also in line
with the observed browning. Land surface temperatures, for example,
were observed to increase over most of the study area. Decreased
cloudiness allowed more solar radiation to reach the plants, which
typically promotes photosynthesis, but in this case it likely posed an
extra stress on the plants from the resulting depletion of soil
moisture.
"Forests of the Congo basin are known to be resilient to moderate
climate change because they have been exposed to dry conditions in the
past few hundred years," Saatchi said. "However, the recent climate
anomalies as a result of climate change and warming of the Atlantic
Ocean have created severe droughts in the tropics, causing major
impacts on forests."
How the changes affect individual plant species in the area remains to
be seen. For example, drier conditions may favor deciduous trees at
the expense of evergreen trees.
"Our assessment is a step toward an improved understanding of how
African rainforests respond to increasing drought," Zhou said. "We
need to consider the complex range of processes affecting different
tropical rainforest species before we can fully assess the future
resilience of tropical forests."
The other authors for this research include Yuhong Tian at I.M.
Systems Group, Inc. at the Center for Satellite Applications and
Research, the science arm of National Oceanic and Atmospheric
Administration's Satellite and Information Service; Ranga Myneni at
Boston University; Philippe Ciais at Laboratoire des Sciences du
Climat et de l'Environnement, Gif sur Yvette Cedex, France; Yi Y. Liu
at University of New South Wales, Australia; Shilong Piao at Peking
University, China; Haishan Chen at Nanjing University of Information
Science and Technology, China; Eric Vermote of NASA's Goddard Space
Flight Center, Greenbelt, Md.; and Conghe Song and Taehee Hwang at
University of North Carolina at Chapel Hill.
NASA monitors Earth's vital signs from land, air and space with a
fleet of satellites and ambitious airborne and ground-based
observation campaigns. NASA develops new ways to observe and study
Earth's interconnected natural systems with long-term data records and
computer analysis tools to better see how our planet is changing. The
agency shares this unique knowledge with the global community and
works with institutions in the United States and around the world that
contribute to understanding and protecting our home planet.
For more information about NASA's Earth science activities in 2014, visit:
http://www.nasa.gov/earthrightnow
For more information about NASA programs, visit:
http://www.nasa.gov
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SOURCE NASA
http://m.digitaljournal.com/pr/1869076
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